The full academic write up will be even longer time coming, but for now here’s a quick summary. A total of 1300 parents completed the survey from 69 countries. A further 700 started the survey but never finished it (presumably interrupted by their babies.)

Conclusions

Babies first smile around 1.5 months and first laugh around 3.5 months. But with some individual variation.

Laughter starts social, babies laugh at/with people not things

Most things get funnier with age

Babies think mummy and daddy are equally funny

Parents think boys laugh more than girls

Peekaboo is universally popular but tickling most reliable way get a baby to laugh

Babies are moral and don’t laugh at other people falling over, so Freud was wrong that child laugh is based on superiority or schadenfreude!